The present invention relates generally to soft switching power inversion and, more particularly, to soft switching power inversion systems for grid interface applications and methods of operation thereof that provide for high efficiency, high frequency switching operation of the power inversion systems.
Inverters are common circuit elements within power electronic circuits for converting a DC power to an AC power. Existing inverters include hard switching and soft switching inverter controls. Hard switching inverter controls are generally considered to be easier to implement than soft switching inverter controls. However, hard switching inverters generally have more losses than soft switching inverters. For example, switching losses in hard switching inverters are generally higher than switching losses in soft switching inverters. Switching losses increase with increasing switching frequency, so switching frequency must be limited to avoid a large amount of switching losses. Hard switching inverters have these greater losses because the transistor is turned on when there is still a voltage across it and/or turned off when there is still a current flowing through it.
Soft switching inverters help to alleviate switching losses by switching the transistor on when the voltage across it reaches zero (zero voltage switching) and/or switching the transistor off when the current flowing through it reaches zero (zero current switching). Soft switching inverters also help to alleviate loss associated with the reverse recovery of the inverter diodes. In many soft switching inverter controls, the phase shift angle is fixed at 180 degrees to obtain a doubled output frequency ripple. However, that 180 degree phase shift angle may cause at least one switch to operate under hard switching inverter controls. As stated above, the hard switching inverter controls can cause a large amount of switching losses, which limit the switching frequency, even with the rest of the inverter switches operating under soft switching inverter controls.
Some soft switching inverters use a phase shift angle less than 180 degrees by calculating the phase shift angle in real time based on the high speed sampling of circulating current. However, these soft switching inverters have a limited soft switching range because the duty cycle is limited. Also, these soft switching inverters must still incorporate large magnetic components because the reduction of the phase shift angle is not enough to reduce the magnetic flux present in the inverter.
It would therefore be desirable to provide a soft switching inverter and method of operation thereof that provides high efficiency operation of the inverter at high frequency switching with an unlimited soft switching range.